1. Field of the Invention
The present invention relates to polymeric films and methods for making the same. More particularly, this invention pertains to polymethylpentene-containing films having improved mechanical, thermal and release properties when exposed to high temperatures.
2. Description of the Prior Art
It is known in the art to produce mulitlayered polymeric films containing a polymethylpentene ("PMP") layer and a thermoplastic layer. For example, U.S. Pat. No. 5,106,692 discloses a delamination resistant structure of layers of PMP and various thermoplastic resins in which a specific adhesive interlayer blend is sandwiched between the layers. The adhesive interlayer blend is a specific blend by a specified weight percent of an ethylene/alpha olefin random copolymer, a functionalized polyolefin, and a tackifier. Such patent discloses that the thermoplastic resins may be polyethylene, polypropylene, nylon, polycarbonate, ethylene/alpha-olefin copolymers, poly(4-methyl-pentene-1), polyacrylate, polymethyl methacrylate, polyvinyl chloride, polyvinylidene chloride, polystyrene, poly-p-xylene, polyesters, and polyamides.
Because of their good water barrier properties, multilayered PMP-thermoplastic films are often laminated to metal sheets for use in the manufacture of corrosion resistant cans for beverages and valve cups for aerosol containers, as in U.S. Pat. No. 5,079,052.
Mulitlayered PMP-polyolefin films are also useful as release films for various high temperature composites such as thermoset composite laminates used in the aerospace industry and printed circuit boards ("PCB"), such as in U.S. Pat. No. 5,080,979. However, because such films typically lose their dimensional stability at temperatures in excess of about 350.degree. F. (177.degree. C.), these films must be cured at lower temperatures for a long period of time. Other known polyolefin release films disadvantageously leave olefin residue on the PCB surface after curing.
It would be desirable to produce a PMP-containing film that retains its dimensional stability and release properties at high temperatures. It would further be desirable to reduce the production cycle time for high temperature composites by using a release film which can be cured both rapidly and without leaving a residue on the surface of the composites.